CITRIC Ai !l> 



CITRIC ACID. 



into carbonic oxide, carbonic acid, uul other product*. By Kulplmru- 

 acid ami bichromate of potaah it is oxidised into formic acid and car- 

 bonic acid. Dilute nitric acid doe* not attack citric acid in tin- eold ; 

 at a high temperature it oxidises it, with the fomiAtion of oxalic, acetic, 

 and carbonic acids. A concentrated aqueous wilutiuii absorb* chlorine 

 very rapidly when exposed to the sunlight : a yellowwh oil U obtained, 

 of a sweet but burning taste, and an irritating odour. Agitated with 

 water, and cooled, the oil solidifies to a maun of crystal*. The action 

 of chlorine on citrate of soda produces different results, an oil <>f 

 complex composition is obtained, containing chloroform. Bromine 

 gives similar results. 



When crystallised citric acid is subjected to destructive dirtillati. .n . it 

 first melts, gives off its water of crystallisation, and at about 850Fahr. 

 it undergoes decomposition ; gases and inflammable vapours are formed, 

 and the residue no longer consists of citric aciil. but is Hconilic arid, 

 called also tauitrtic nr alriilir arid (C lf H,Q,, 3HO). If the heat be 

 -till increased, dense Tapours appear, which condemn* to oily drops, and 

 afterwards solidify to a crystalline mass of ilaconic acid (C 10 H 4 O e , 1 H ( ) ) ;' 

 and if these crystals be repeatedly distilled, an oily mass of anhydrou* 

 citraconic arid (C 10 H 4 O.), called also pyrocitric and citriblc acid, in 

 obtained, which does not solidify. 



Citric acid is extensively used as a mordant in calico-printing. It is 

 used in pharmacy for the preparation of syrups and lemonade. Mixed 

 in small proportion with sugar and aromatic substances, it serves to 

 form dry lemonade. 



The crystallised acid loses two equivalent* of water when heated 

 below 212. Ita composition then is C,,H.O U = C.,11,0,., 8HO. 



Citric acid is a triUwic acid, and U capable of forming three series of 

 mlts. It contains the tribasic radical retryl, C,.H S 0,, which, when 

 united with three equivalents of oxygen, forms " the anhydrous acid, 

 l^.H.O,, ; and united with three equivalents of chlorine, forms the 

 chloride of clltyl, C,,H.O,, Cl,. 



The composition of the citrates may be thus written : 



Neutral 

 Acid . 

 Acid 



trlmetalllc citrates . 

 bimetallic citrates 

 monometallic citrates 



CiiH.O,,, SMO 

 C lt H,0 M , (2MO + HO) 

 C II H HI ( Mo + 2HO ) 



Citric acid also forms polybasic salts ; with lead this is more espe- 

 cially the case. Their general formula may be written 



c ii n n. "MO + iMO. 



The alkaline citrates are very soluble in water, and crystallisable 

 with more or less facility. Like the tartrates, they prevent the pre- 

 cipitation of the salts of iron, manganese, &c., by alkalies. The citrates 

 of magnesia, zinc, iron, cobalt, nickel are soluble. The neutral citrates 

 of baryta, strontia, lime, on the other hand, are very little soluble ; 

 the acid salts more so. The citrate, and ammonio-citrate of iron, are 

 frequently used in medicine. Their exact composition is not known. 



Cilrie tAert. The ethers of citric acid correspond to citrates in 

 which the metal is replaced by its equivalent of methyl, ethyl, or am yl. 

 The acid ethers form salts with bases : 



Mrthjlocitric ether 

 BlmethTlocitric ether 



c iH,,0 14 = 

 C,.H M 0., = 



Neutral citrate of meibjrl C,.H,,O 14 

 Neutral cltrmU of elhjrl C,.H,.O 14 



c n u ii. c,n,o 

 an o 



C.,11.,0,,, 2C.H.O 



II II 



C,,1I S 11 ,8C,U J 



C IH.O M , ic.u.o 



Citric ether, or neutral citrate of ethyl, is best prepared by saturating 

 an alcoholic solution of citric acid with hydrochloric acid. The free 

 acid U neutralised with carbonate of soda, and the residue treated with 

 ether. On the evaporation of the ether, the citrate of ethyl is left 

 as a yellowish, transparent, heary oil, which cannot be distilled without 

 decomposition. 



Amybcilrie arid ^'"'^ 



ing citric acid with omylic alcohol, is a viscous liquid presenting traces 

 of crystallisation. It forms crystollisable salts with alkalies Arid 



C..H.O,., C IO H,.O 1 

 rife* of eHyt arf ,./< C,.H M U = 1 1 j* is obtained 



, H,,0 1 

 C.H.OJis 



by saturating an alcoholic solution of the preceding compound with 

 hydrochloric acid. 



Amidn and anilidfi of citric arid. The only amide 'of citric acid 

 known is eitramidt (C lt H,,N,0,), prepared by the action of ammo- 

 nia on citnc ether. It represents neutral citrate of ammonia, minus 

 fix equivalents of water. 



C.iU.O,, -no = C 1 ,N,H I1 0.. 

 Citrainide may be regarded as being 3 eq. of ammonia, in which the 



C HO**! 

 tribasic radical rtfrj/f (C,,H,O.) replaces 8 eq. of hydrogen " V, l r 



Being a tribasic acid, citric acid ought to form amide compounds 



wwspooding to each of iu ammonia salts. These have not been 



Pebal has investigated the corresponding anilide com- 



poo**- _y*V * 'ined by the action of aniline on citric acid 



ader varying conditions. They are of complex constitution and great 



theoretical interest. For a full account the reader is referred to the 

 original paper* in Kit-big's ' Annalen,' . uiglinh edii 



Gmelin's ' Handbook of Chemistry." A few only aro enumerated 

 here. 



Cilraailide, or phmylcitramide ((' 4 ,N,H,,0,), U tribanic citrate of 

 aniline, minus 6 atoms water. 



C,.H t (C It H,K),O u 6110 = C..N,H,,0. 

 Tribasic citrate of aniline. Citranilidc. 



It may be considered to be derived from 8 atoms Nil,, in wl.i, h :> 

 atoms H ore replaced by the radical citryl, and by 3 atoms of ph,-n\ 1 



( " H S J. 



Citrobiantle, or pliexi/lcitramlde (C^H^N.O,), a neutral l*.ly. t 

 from bibasic citrate of aniline by the loss of 8 atoms v 



C lf II,O, 4 , 2C lt n,N 6HO = C,,H 14 N,O, 

 Bibasic citrate of aniline. Citrobianile. 



It may be viewed as a diamide, tliat is, 2 eq. of ammonia, in whieh 3 

 atoms hrdrogen ore replaced by citryl, and 2 atoms by 2 of phenyl 



Citrobianllic acid (C K> N,H 1 ,0 10 ) is bibasic citrate of aniline 

 water. It forms crystalline salts. 



C,,n,0 1 ,,2C, a H,N 4HO = C,.N,H 1 .0 I . 



Bibasic citrate of aniline. CltroblaniUc acid. 



(.'itninilic acid C^NH^O,,,, obtained by the action of heat on mono- 

 basic citrate of aniline. 



C la NH., C 15 H.0 lt 4HO = C t ,Nn ll O,.. 



It may be derived from the type, hydrated oxide of ainin 



j| | O, in which 3 at ore replaced by citryl, and 1 at. H by phony!, 

 N,C U H,. C n H.O 



Cltloridt of ritryl (C.jH.O.Cl,). ^Ticn citric acid is treate<l with 

 pentjichloride of phosphonis it becomes heated, and yields a mixture 

 of oxychloride of phosphorus and o.ri/cJi/<>rofilrir arid, t'uHjOj.Cl,, a 

 body crystallising in long silky needles, and which, with water, i. 

 rates citric acid and hydrochloric aci.t. The mixture further heated, 

 gives off hydrochloric acid and chloride of i-HnjI, C,.,H <>.< 

 to lie fiirmed. 



Acids derived from citric acid by the action of heat. 



Aconitic acid, C^HnO,, = C.jH.O,, 8HO. This acid is found a lime 

 Holt iu many sj-ecies of aconite. It U also found in (ifiiisrium, mid \\.,- 

 termed tqmtetic acid. It is formed from citric acid by heat, and thi^ 

 is its best source. Citric acid is distilled until crystalline ntri:o appear 

 in the receiver. The residue dissolved in alcohol, and saturated with 

 hydrochloric acid, forms aconitic ether, which treated by potash yield.-, 

 aconitateof potash. This is precipitated by a soluble lead salt, and 

 the aconitate of lead formed decomposed by sulphuretted hydrogen, 

 and the nitrate from the sulphide of lead evaporated. 



It forms indistinct crystals, very soluble in alcohol -dud ether. It is 

 formed from citric acid by simple loss of water. 



C.,11,0,, 2HO = CnH.O,,! 



Citric acid. Aconitic acid. 



Aconitic acid when heated assumes an ambei colour, melt* and buiU 

 at ;i'20 Kidir. It then decomposes into carbonic acid, and a new 

 itacotii'- H'-'nl. which may be condensed in the receiver. 

 C..H.O., a ICO, + C..II.O. 



Ac, .niiit Idd. 



lUconlc acid. 



By this decomposition aconitic acid is distinguished from its ixomers, 

 fiimaric and maleic acids. 



Aconitate of lime, placed in water in contact with decaying cheese, 

 is changed into succinic acid. acid, it forms three series 



of salts monometallic \K i -t .'Hui bimetallic,- C..H.O . 



(2MO + HO) ; and trimetallic, C.^.O,, SMO. They ore little known) 

 and arc of no great interest. 



Aconitic ether (C,,H,0,, 8C,H,O), obtained as above in the prepara- 

 tion of aconitic acid, is a colourless aromatic liquid, with a very l>itter 

 taste. It is rather heavier than water and boils at 425 Fain . 



By the action of aniline on nconitic acid compounds are obtained 

 analogous to those derived from citric acid. 



Pyrocilric acidi. 1'nder this name Gerhardt classes three isomeric 

 acids derived from citric acid. They are itoconic, citraconic, and 

 mesaconic acids. 



